Method and apparatus for reducing total pressure loss in a turbine engine

ABSTRACT

A method and apparatus for reducing total pressure loss in the exhaust of a combustion device via an axial diffuser having no turning vanes, support struts, rods, or other obstructions to exhaust flow. The axial diffuser includes an inner wall and an outer wall each having a turn radius and forming an annular cross section having increasing cross-sectional area in the downstream direction of flow, the flow being transitioned from axial to radial direction thereby. The diffuser is supported in the plenum by rods, struts or a cradle; from a stand surrounding the axial diffuser via struts or rods; or from existing diffuser support structure by web stiffeners. The diffuser flow path turn radius of the outer wall ranges from about 50-95% of the radial distance from the inner wall to a wall of the exhaust plenum, and of the inner wall ranges from about 10-70% of this distance.

This application claims priority from U.S. Provisional Application Ser.No. 60/473,442 filed May 28, 2003. The entirety of that provisionalpatent application is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to turbine engine exhaust systems andmore particularly to turbine engine exhaust systems containing axialdiffusers that reduces pressure loss.

2. Background of the Technology

Typical combustion fired gas turbines consist of a compressor,combustion system, a power turbine, and an exhaust system, such as theexhaust system 1 shown in FIG. 1. A typical exhaust system 1 includesaerodynamic struts 2 (as further shown in closeup in FIG. 2) and a90-degree axial to radial diffuser (axial to radial turn and supportrods for a radial diffuser 30 are shown in FIG. 3) disposed within aplenum 4, followed by either a silencer 5 (plenum 4 and silencer 5 arefurther shown in FIG. 4) in a simple cycle system or a heat recoverysteam generator in a combined cycle system. Also shown in FIG. 1 is apower turbine exit annulus/inlet to exhaust system 8. Note that theaxial to radial turn and support rods, while contained within theexhaust system 1, are not visible in FIG. 1.

As shown in FIG. 3, the axial to radial diffuser 30 (alsointerchangeably referred to herein as an axial to radial turn) turns theflow from an axial direction to a radial direction to fill the plenum 4,as shown in FIG. 1. The axial to radial turns can be oriented in anydirection, left right or top, depending upon the layout of the balanceof the plant. Total pressure losses associated with these turns areirreversible and unrecoverable and therefore represent a reduction inthe overall efficiency of the turbine. Further, the connection pointsand other features of the rods or struts and turning vanes associatedwith such exhaust systems often crack, requiring welding or similarrepair, or require other maintenance.

Referring now to FIG. 5, a conventional axial to radial diffusergenerally includes aerodynamic turning vanes 50 and support struts orrods 51. The support struts/rods 51 support both the turning vanes 50and the outer radial wall 52 of the diffuser. The intent of the turningvanes 50 is to turn the flow from an axial direction A (as it leaves thepower turbine last stage) to a radial direction B, such that the flowfills the plenum as efficiently as possible. Note that small, tightradius turns C are typically used for the turning vanes 50 of aconventional diffuser, as further shown in FIG. 6.

Attempts to improve upon conventional diffusers have been made. Theprior state of the art [see, e.g., Norris, “Test Program for HighEfficiency Turbine Diffuser—Project Summary (California EnergyCommission Energy Innovations Small Grant Program, available ateisg.sdsu.edu/Fullsums/01-29.htm (last visited on May 19, 2003)]involves “inserting aerodynamic vanes and devices placed inside theexhaust diffuser” to “reduce backpressure on the turbine.” The smallgains achieved using these techniques are not economically feasible toimplement. Among other reasons, this approach does not work because itis impossible to match the orientation of the aerodynamic vanes to theflow for the full range of turbine operating conditions. Other attemptsat improving the conventional exhaust system are illustrated in U.S.Pat. Nos. 5,188,510, 5,603,604, 5,813,828 and 5,340,276.

SUMMARY OF THE INVENTION

The present invention overcomes the above mentioned problems with theprior art, as well as others, by providing a method and apparatus forreducing total pressure loss in the exhaust portion of a combustionsystem. An embodiment of the method and apparatus include one or more ofthe following features: 1) removing the axial to radial turning vanesand any other devices of the prior art for conditioning or improving theflow field between the hub wall and outer radial wall of the axialdiffuser aft of the main exhaust struts; 2) removing any support strutsor rods and any other blockages or obstructions that interact with theflow between the hub wall and outer radial wall of the axial diffuseraft of the exhaust struts; and 3) transitioning the axial diffuser flowpath from an axial to a radial direction using a radius turn.

In an embodiment of the present invention, the transitioned axialdiffuser flow path includes a turn radius in an inner wall (alsointerchangeably referred to herein as “the hub surface”) of the axialdiffuser ranging preferably between about 50% and 95% of the radialdistance from the hub surface of the axial diffuiser to the nearest wallof the exhaust plenum. In an embodiment of the present invention, theflow path also includes a turn radius in the outer radial surface of theaxial diffuser, the turn radius of the inner radial surface beingpreferably between about 10% and 70% of that of the outer radial turn.Depending on particular advantages for each embodiment, the turn radiusof the hub surface of the axial diffuser may or may not be concentricwith the turn radius of the outer radial surface of the axial diffuser.

In embodiments of the present invention, the end of the outer surface ofthe axial diffuser with the aforementioned turn radius is supported viaa support structure in any number of ways, including: a) from theexhaust plenum floor by rods, struts or a cradle; b) from a standsurrounding the axial diffuser by one or more struts or rods; or c) fromthe existing diffuser support structure by web stiffeners attached tothe outside surface of the diffuser wall.

The approach of the present invention performs better than in the priorart at least in part because the resultant static pressure in theexhaust plenum reaches a value equal to the static pressure that occursat the inside of the turn from the axial to radial direction at the exitof the turn. The flow rate and the radius of curvature of the turn setthe pressure at this location. The larger the radius of the turn, thehigher the resultant pressure and the greater the pressure recovery.

Using the present invention, turbine efficiency and output can beimproved on the order of 1 percent. This amount of improvement iseconomically feasible to achieve, given the lack of expensiveaerodynamically shaped hardware. The only hardware required to implementthis design is a new smooth radius axial to radial turn, which is aninexpensive part to manufacture and install in the turbine or othercombustion device.

In addition, the present invention reduces maintenance and repairassociated with the struts or rods and turning vanes of prior art axialdiffusers.

Additional advantages and novel features of the invention will be setforth in part in the description that follows, and in part will becomemore apparent to those skilled in the art upon examination of thefollowing or upon learning by practice of the invention.

BRIEF DESCRIPTION OF THE FIGURES

In the drawings:

FIG. 1 shows an exemplary exhaust system for a typical combustion firedgas turbine, the turbine consisting of a compressor, combustion system,a power turbine, and an exhaust system;

FIG. 2 contains a view of an exemplary aerodynamic strut section for theexhaust system of FIG. 1;

FIG. 3 presents a view of axial to radial turn and support rod featuresfor an exemplary diffuser for use with the exhaust system of FIG. 1;

FIG. 4 shows a view of an exemplary plenum and silencer for the exhaustsystem of FIG. 1;

FIG. 5 presents a view of a conventional axial to radial diffuser thatincludes aerodynamic turning vanes and support struts or rods;

FIG. 6 contains a view of a conventional diffuser, showing the small,tight radius turns that are typically used for turning vanes;

FIG. 7 is a cutaway view of an exemplary diffuser in accordance with anembodiment of the present invention;

FIG. 8 shows a closeup view of the turn radius of the inner radial ofthe diffuser of FIG. 7;

FIG. 9 contains a closeup view of the turn radius of the outer radial ofthe diffuser of FIG. 7;

FIG. 10 is a cutaway view the diffuser of FIG. 7;

FIG. 11 shows a cross-sectional view of a diffuser, in accordance withan embodiment of the present invention;

FIG. 12 contains another view of the diffuser of FIG. 11, with the hubwall of the diffuser indicated;

FIG. 13 presents a view of the diffuser of FIG. 11, with the outer wallof the diffuser indicated;

FIG. 14 is another view of the diffuser of FIG. 11, with perpendiculardistance from the hub of the diffuser to the nearest parallel wall ofthe exhaust plenum indicated;

FIG. 15 shows the radius turn of the hub wall of the diffuser, inaccordance with an embodiment of the present invention;

FIG. 16 shows the radius turn of the outer wall of the diffuser, inaccordance with an embodiment of the present invention;

FIGS. 17-19 present views of the end of the outer surface of the axialdiffuser supported from the exhaust plenum floor by rods, struts or acradle, in accordance with an embodiment of the present invention;

FIGS. 20-22 show views of the end of the outer surface of the axialdiffuser supported from a stand surrounding the axial diffuser by one ormore struts or rods, in accordance with an embodiment of the presentinvention; and

FIGS. 23-25 contain views of the end of the outer surface of the axialdiffuser supported from the existing diffuser support structure by webstiffeners attached to the outside surface of the diffuser wall, inaccordance with an embodiment of the present invention.

DETAILED DESCRIPTION

The method and apparatus of one embodiment of the present invention,which reduces the total pressure loss in the exhaust portion of aturbine or other combustor includes one or more of the followingfeatures: 1) completely removed axial to radial turning vanes and anyother devices used for or intended to condition or improve the flowfield between the hub wall and outer radial wall of the axial diffuseraft of the main exhaust struts; 2) completely removed support struts orrods and any other blockages or obstructions that interfere or otherwiseinteract with the flow between the hub wall and outer radial wall of theaxial diffuser aft of the exhaust struts; and 3) transitioning of theaxial diffuser flow path from an axial to a radial direction using alarge radius turn.

In particular, in one embodiment, the transitioned axial diffuser flowpath includes a turn radius in an inner wall (also interchangeablyreferred to herein as “the hub surface”) of the axial diffuser rangingpreferably between about 50% and 95% of the radial distance from the hubsurface of the axial diffuser to the nearest wall of the exhaust plenum.In an embodiment of the present invention, the flow path also includes aturn radius in the outer radial surface of the axial diffuser, the turnradius of the inner radial surface being preferably between about 10%and 70% of that of the outer radial turn. Depending on particularadvantages for each embodiment, the turn radius of the hub surface ofthe axial diffuser may or may not be concentric with the turn radius ofthe outer radial surface of the axial diffuser.

References will now be made in detail to embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings.

One embodiment of a diffuser according to the present invention isillustrated in FIGS. 7-16. In the embodiment of FIGS. 7-16, both theturning vanes and the support struts/rods have been removed and largeradius turns have been included on both the hub and outer walls of thediffuser. As discussed above, not all features are present in allembodiments of the invention. For example, in some embodiments, theturning vanes are removed without removing the support struts. In otherembodiments, the turning vanes and the struts are removed, while one orboth of the diffuser surfaces are provided with a small radius, ratherthan a large radius. Other combinations of the features set forth aboveare also possible in other embodiments of the present invention.

As shown in FIG. 7, in an embodiment of the present invention, a rotorshaft 71 traverses the center of an axial diffuser 70. The shaft 71,which is driven, for example, by exhaust flow via one or more bladesconnected to the shaft 71, rotates and is optionally connected to anoutput device, such as a generator. The diffuser 70 includes a diffuserinner radial wall 72 and a diffuser outer radial wall 73.

As shown in the closeup of the diffuser 70 contained in FIG. 8, thepresent invention includes a diffuser inner wall 72 having a radius turnR₁, such as a large turn radius. Similarly, as shown in FIG. 9, theouter wall 73 of the diffuser 70 also has a radius turn R₂, such as alarge turn radius. As a result of the features shown in FIGS. 7-9, thisembodiment of the present invention removes or reduces the need foraxial to radial turning vanes, support struts, rods, or gussets, etc.,of the prior art (see, e.g., FIG. 5), and provides for an unobstructed,“clean” flow path between the inner and outer walls 72, 73 of thediffuser 70.

FIG. 10 shows another cutaway view of a diffuser 70, in accordance withan embodiment of the present invention. In the cross-sectional view ofthe diffuser 70 shown in FIG. 11, the axial diffuser inlet 110 isannular in a cross section perpendicular to the direction of the exhaustcenterline C, with the inlet 110 widening in cross-sectional areadownstream of flow direction F, as flow proceeds from the exhaust of thepower turbine or other combustion device into the plenum.

FIG. 12 contains another view of the diffuser 70 of FIG. 11, with acentral portion of the inner wall 120 of the diffuser 70, indicated.FIG. 13 presents a view of the diffuser 70 of FIG. 1, with the outerwall 73 of the diffuser 70 indicated.

As shown in FIG. 14, in an embodiment of the present invention, theradial distance D extends from the portion of hub wall 120 of the axialdiffuser 70, which is approximately parallel to the direction of thecenterline C, to the nearest cross-sectionally approximately parallelwall 140 of the exhaust plenum. In one embodiment of the presentinvention, the nearest such wall 140 is the bottom side of the exhaustplenum, as shown in FIG. 14.

FIG. 15 shows the radius turn RI of the hub wall 72 of the diffuser 70.The radius of hub wall radius turn R₁, for example, is between about 50%and 95% of D.

Similarly, as shown in FIG. 16, the radius turn R₂ of the outer wall 73of the diffuser 70, together with the hub wall 72, form a flow path thatallows the exhaust system to transition the exhaust flow from an axialdirection AD to a radial direction RD via the radius turns. The radiusof inner wall radius turn R₁, for example, is between about 10% and 70%of the radius of outer wall radius turn R₂.

The end of the outer surface of the axial diffuser with theaforementioned turn radius can be supported any number of ways,including: a) from the exhaust plenum floor by rods, struts or a cradleas shown in FIGS. 17-19; b) from a stand surrounding the axial diffuserby one or more struts or rods as shown in FIGS. 20-22; or c) from theexisting diffuser support structure by web stiffeners attached to theoutside surface of the diffuser wall as shown in FIGS. 23-25; or by anycombination of the above. In addition, in some variations, the outersurface is supported by rods or struts, absent turning vanes. The outersurface is also supported, in other variations, by a non-attachedexternal mechanism, such as a portion of a turbine abutting or otherwisesupporting the outer surface. These various combinations of supportfeatures, collectively and individually, are interchangeably referred toherein as “a support mechanism.”

FIGS. 17-19 show cutaway views of an axial diffuser 170 supported by anexemplary bottom cradle 172. Similarly, one or more elements of thediffuser 170 may be supported by rods or struts. FIGS. 20-22 containcutaway views of an axial diffuser 200 supported by an exemplary fullcradle 201. FIGS. 23-25 present cutaway views of an axial diffuser 230supported by an existing diffuser support structure 231 (the indicatedstructure in FIGS. 23-25, having opposite end [not shown] is attached tothe opposite wall of the plenum at the inlet to the exhaust system) byweb stiffeners 232 attached to the outside surface of the diffuser wall233.

Example embodiments of the present invention have now been described inaccordance with the above advantages. It will be appreciated that theseexamples are merely illustrative of the invention. Many variations andmodifications will be apparent to those skilled in the art.

1. An axial diffuser, comprising: an inner wall connected to an exhaustplenum, the inner wall having an inner wall radius turn; an outer wallhaving an outer wall radius turn; and a support mechanism supporting theouter wall; wherein the inner wall and the outer wall form a flow pathfree of turning vanes.
 2. The diffuser of claim 1, wherein has acircular cross-sectional shape.
 3. The diffuser of claim 2, wherein theinner wall has an opening, and wherein a shaft is receivable in theinner wall opening in a direction along a centerline within the openingin the inner wall.
 4. The diffuser of claim 3, wherein the inner wallincludes a first inner wall portion, the first inner wall portionextending in a direction generally parallel to the centerline.
 5. Thediffuser of claim 1, wherein the outer wall radius turn is a largeradius turn.
 6. The diffuser of claim 5, wherein the large radius turnof the inner wall has a radius between about 50% and 95% of aperpendicular distance from the first inner wall portion to a wall ofthe exhaust plenum.
 7. The diffuser of claim 6, wherein theperpendicular distance is a minimum.
 8. The diffuser of claim 1, whereinthe outer wall has a circular cross-sectional shape.
 9. The diffuser ofclaim 6, wherein the outer wall radius turn is a large radius turn. 10.The diffuser of claim 9, wherein the large radius turn of the inner wallhas a radius between about 10% and 70% of the radius of the outer radialturn.
 11. The diffuser of claim 1, wherein the support mechanismcomprises a connection between a wall of the exhaust plenum and theouter wall.
 12. The diffuser of claim 11, wherein the connectioncomprises one selected from a group consisting of rods, struts, or acradle.
 13. The diffuser of claim 11, wherein the connection comprises astand surrounding the axial diffuser.
 14. The diffuser of claim 11,wherein the connection comprises at least one web stiffener attached toa wall of the axial diffuser.
 15. The diffuser of claim 1, wherein thesupport mechanism is external to the flow path.
 16. The diffuser ofclaim 1, wherein the support mechanism comprises an extension fromturbine.
 17. The diffuser of claim 1, wherein the cross-sectional areaof the flow path increases in size in a downstream direction of exhaustflow through the flow path.
 18. The diffuser of claim 3, wherein thecross-sectional area of the flow path increases in size in a downstreamdirection of exhaust flow through the flow path, and wherein the shaftis a rotor shaft.
 19. The diffuser of claim 18, wherein the rotor shaftis rotated by the exhaust flow.
 20. The diffuser of claim 19, whereinthe rotor has at least one attached blade.
 21. The diffuser of claim 1,wherein the inner wall radius turn is concentric with the outer wallradius turn.
 22. The diffuser of claim 1, wherein the flow path isunobstructed by at least one selected from a group consisting of radialturning vanes, support struts, and rods.
 23. The diffuser of claim 1,wherein the annular flow path transitions the exhaust flow from an axialdirection to a radial direction.
 24. The diffuser of claim 1, whereinthe flow path has a generally annular cross-sectional shape.
 25. Anaxial diffuser for a combustion device exhaust component, the exhaustcomponent including an exhaust plenum having at least a first plenumwall and a second plenum wall, the diffuser comprising: an outerdiffuser wall having a circular cross-sectional shape; an inner diffuserwall attached to the first plenum wall, the inner diffuser having acircular cross-sectional shape and an inner opening, wherein the innerdiffuser wall is situated such that the inner diffuser wall and theouter diffuser wall form a flow path therebetween, the flow path beingunobstructed by turning vanes.
 26. The axial diffuser of claim 25,wherein the flow path has a generally annular cross-sectional shape andcross-sectional area, the area of the annular cross-sectional areaincreasing with downstream direction of exhaust flow in the flow path27. The axial diffuser of claim 25, further comprising: a rotorextending through the inner opening of the inner diffuser wall.
 28. Thediffuser of claim 26, wherein the inner wall includes a first inner wallportion and a second inner wall portion, the second inner wall portionincluding a radius turn.
 29. The axial diffuser of claim 28, wherein theradius turn of the inner wall is a large radius turn having a radiusbetween about 50% and 95% of a perpendicular distance from the firstinner wall portion to the second plenum wall.
 30. The diffuser of claim28, wherein the outer wall includes a radius turn.
 31. The diffuser ofclaim 30, wherein the inner wall radius turn and the outer wall radiusturn cooperate to transition the exhaust flow from an axial direction toa radial direction.
 32. The diffuser of claim 29, wherein the outer wallincludes a large radius turn, the large radius turn of the inner wallhaving a radius between about 10% and 70% of radius turn of the innerwall large radius turn.
 33. A method for reducing total pressure loss inthe exhaust flow of a combustion device having an exhaust plenum, themethod comprising: forming a flow path unobstructed by turning vanes,the flow path being located within an axial diffuser in the exhaustplenum, wherein the flow path has an increasing cross-sectional area indownstream direction of flow therethrough, wherein the axial diffuserincludes an inner wall having a radius turn and an outer wall having aradius turn, the inner wall being attached to a wall of the exhaustplenum and the outer wall being attached to the exhaust plenum via asupport mechanism external to the flow path; transmitting the exhaustflow through the axial diffuser; and transitioning the exhaust flow froman axial direction to a radial direction.